JPH1050342A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery with high capacity and low self-discharge rate. SOLUTION: This battery is composed by containing 1,3,2-di-oxaphosphoran-2- oxide dielectric or propane sultone or butane sultone in the range of a mixture rate of 5% or more and 50% or less in an electrolyte solvent. Here, a battery self-discharge rate can be reduced by adding the above substance to the electrolyte solvent of this battery. This battery is composed of a negative pole cap 1, a negative pole pellet and a polypropylene-based thin film separator 3, a positive pole pallet 4, a gasket 5 and a positive pole can 6. The positive pole pellet 4, the separator 3 and the negative pole pellet 2 are laminated in this order, electrolyte is injected and cauked, and a lithium ion coin type battery of 200mm in diameter and 2.5mm in thickness whose shape is the same as CR2025 type is prepared.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery having a high capacity and a low self-discharge rate.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices such as video cameras, demand for secondary batteries that can be used repeatedly instead of disposable primary batteries has been increasing.
Most of the secondary batteries currently used are nickel cadmium batteries using an alkaline electrolyte. However, since the voltage of this battery is about 1.2 V, it has been difficult to further improve the energy density of the battery. Further, the self-discharge rate at room temperature was as high as 20% or more in one month.

[0003] Therefore, by using a non-aqueous solvent for the electrolyte and using a light metal such as lithium for the negative electrode, the voltage is increased to 3 V or more to increase the energy density, and further, the non-aqueous electrolyte having a low self-discharge rate is used. Secondary batteries have been considered.
However, such a secondary battery has a disadvantage that lithium metal or the like used for the negative electrode grows in a dendrite shape by repeated charge and discharge and comes into contact with the positive electrode, and as a result, a short circuit occurs inside the battery and the life is short. It was difficult to put it to practical use.

For this reason, a non-aqueous electrolyte secondary battery in which lithium or the like is alloyed with another metal and this alloy is used for a negative electrode has been studied. However, also in this case, there is a disadvantage that the alloy becomes fine particles due to repeated charge and discharge, and the life is also shortened.

[0005] Further, in order to improve the above-mentioned drawbacks, for example, as disclosed in Japanese Patent Application Laid-Open No. 62-90863, a non-aqueous electrolyte secondary battery using a carbonaceous material such as coke as a negative electrode active material. Has been proposed. Since this secondary battery does not have the above-mentioned disadvantages of the negative electrode, it has excellent cycle life characteristics. As the positive electrode active material, LixMO ₂ (M represents one or more transition metals, and x represents 0.05 or more, as disclosed by the present inventors in JP-A-63-135099. (1.10 or less), the battery life is improved and a non-aqueous electrolyte secondary battery with high energy density can be formed.

However, a non-aqueous electrolyte secondary battery using the above-described carbonaceous material as a negative electrode active material has superior cycle life and safety compared to a secondary battery using metal lithium or the like as a negative electrode active material. However, there is a problem that the self-discharge rate is inferior.

[0007]

Accordingly, an object of the present invention is to improve the self-discharge rate of a nonaqueous electrolyte secondary battery using a carbonaceous material as a negative electrode active material and having excellent cycle life and safety, An object of the present invention is to provide a nonaqueous electrolyte secondary battery having a high capacity and a small capacity deterioration.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in a non-aqueous electrolyte secondary battery, 1,3,2-dioxaphosphorane-2-ether is used as an electrolyte solvent.
The non-aqueous electrolyte secondary battery includes an oxide derivative, propane sultone, or butane sultone in a mixing ratio of 5% or more and 50% or less to solve the above problem.

[0009] The self-discharge rate of the battery can be reduced by adding the above-mentioned substances to the electrolyte solvent of the non-aqueous electrolyte secondary battery.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present inventor has shown that a non-aqueous electrolyte secondary battery having a high capacity and a low self-discharge rate can be manufactured even using the carbonaceous material described in the prior art. The solvent for the electrolytic solution was found through intensive studies.

First Embodiment First, as a first embodiment, the solvent for the electrolyte is 1,
A non-aqueous electrolyte secondary battery using an organic solvent that can be mixed with a 3,2-dioxaphosphorane-2-oxide derivative will be described.

In a nonaqueous electrolyte secondary battery using a carbonaceous material as a negative electrode active material, a carbon powder obtained by sintering a raw material at a predetermined temperature and atmosphere or pulverizing after firing is used as the carbonaceous material.

Petroleum pitch as a raw material of the carbonaceous material;
Binder pitch, polymer resin, green coke, etc.
In addition, completely carbonized graphite, pyrolytic carbons, cokes (coal coke, pitch coke, petroleum coke, etc.), carbon black (acetylene black, etc.), glassy carbon, calcined organic polymer materials (organic polymer The material is fired at an appropriate temperature of 500 ° C. or more in an inert gas stream or vacuum), pitches containing carbon fiber and the like and a resin component, and highly sinterable resins such as furan resin and divinyl After a mixture is prepared using benzene, polyvinylidene fluoride, polyvinylidene chloride or the like, a fired body is prepared, and after adjusting the particle size such as pulverization, it can be used. It is also possible to use a material such as a lithium composite oxide which can dope and dedope lithium.

On the other hand, an active material containing LixMO ₂ is used for the positive electrode. Here, M represents one or more transition metals, preferably one of Co, Ni, and Fe.
x is 0.05 or more and 1.10 or less. Such active materials include LiCoO ₂ , LiNiO ₂ , LiNiyCo
(1-y) O ₂ (provided that 0 <y <1). Alternatively, LiMn ₂ O ₄ can be used.

The composite oxide is obtained by, for example, mixing carbonates such as lithium, cobalt, and nickel according to the composition and firing the mixture in an oxygen-containing atmosphere at a temperature in the range of 600 ° C. to 1000 ° C. The starting materials are not limited to carbonates, but can be similarly synthesized from hydroxides and oxides.

The solvent for the electrolytic solution is also the same as the 1,3,2-
When a dioxaphosphorane-2-oxide derivative is used, any organic solvent that can be mixed therewith can be used. The electrolyte is dissolved in this mixed solvent and used as the electrolyte. Accordingly, examples of the organic solvent include esters such as propylene carbonate, ethylene carbonate and γ-butyl lactone; ethers such as diethyl ether, tetrahydrofuran, substituted tetrahydrofuran, dioxolan, pyran and derivatives thereof, dimethoxyethane, and diethoxyethane; 3-substituted-2-oxazolidinones such as -methyl-2-oxazolidinone, sulfolane,
Examples thereof include methylsulfolane, acetonitrile, propionitr and the like, and these may be used alone or as a mixture of two or more. Also, as the electrolyte, lithium perchlorate,
Lithium borofluoride, lithium hexafluorophosphate, lithium aluminate, lithium halide, lithium trifluoromethanesulfonate, imide salts and the like can be used.

The chemical formula of the 1,3,2-dioxaphosphorane-2-oxide derivative is shown in FIG. 2, where R1, R2 and R3 are H, CH _3, OCH
Represents a functional group such as ₃ . FIG. 3 shows the chemical formula of 1,3,2-dioxaphosphorane-2-oxide.

First, a positive electrode pellet was prepared as follows. As the positive electrode compound, 0.5 mol of lithium carbonate and 1 mol of cobalt carbonate were mixed and calcined in air at 900 ° C. for 5 hours to obtain LiCoO ₂ . This LiCoO ₂
Was ground to obtain a powder having an average particle size of 10 μm. Next, 91 parts by weight of this LiCoO ₂ , 6 parts by weight of graphite as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder were added, and N-methylpyrrolidone was added as a dispersant to the mixture. Paste created. Thereafter, the paste was dried and pressed to obtain a positive electrode pellet having a volume density d of 3.5 g / cm ² and a diameter of 15.5 mm.

Next, a negative electrode was prepared as follows. The carbon material uses pitch coke and is ground to reduce the average particle size to 3.
The material having a thickness of 0 μm is treated in nitrogen at 1000 ° C.
Impurities were removed. 90 parts by weight of this carbon material and 10 parts by weight of polyvinylidene fluoride as a binder were mixed, and N-methylpyrrolidone was added as a dispersant to prepare a paste. Thereafter, the paste was dried to obtain negative electrode pellets having a diameter of 16.0 mm.

FIG. 1 shows an example of the configuration of a secondary battery using the above-described positive and negative electrode pellets. The secondary battery includes a negative electrode cup 1, a negative electrode pellet 2 made of the negative electrode active material, a thin film separator 3 made of polypropylene, the above-described positive electrode pellet 4, a gasket 5, and a positive electrode can 6.
The positive electrode pellet 4, the separator 3, and the negative electrode pellet 2 are laminated in this order, and an electrolyte is injected, caulked, and CR202
A lithium ion coin battery 10 having the same shape as the type 5 and a diameter of 20 mm and a thickness of 2.5 mm was prepared.

Example 1 As an electrolyte for the lithium ion coin type battery 10,
Mixing ratio of 1,3,2-dioxaphosphorane-2-oxide and diethyl carbonate (DEC) 50: 5
A mixture obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixed solution of 0 was used.

Embodiment 2 As an electrolyte for the lithium ion coin type battery 10,
1-chloro-1,3,2-dioxaphosphorane-2
A mixture ratio of oxide and diethyl carbonate of 50:
A mixture obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixed solution of 50 was used.

Example 3 As an electrolyte for the lithium ion coin-type battery 10,
2-methoxy-1,3,2-dioxaphospholane-
Mixing ratio of 2-oxide and diethyl carbonate 5
A solution obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixture of 0:50 was used.

Example 4 As an electrolyte for the lithium ion coin battery 10,
4-methyl-1,3,2-dioxaphosphorane-2
A mixture ratio of oxide and diethyl carbonate of 50:
A mixture obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixed solution of 50 was used.

Embodiment 5 As an electrolyte of the lithium ion coin battery 10,
A mixture of 2,4-dimethyl-1,3,2-dioxaphosphorane-2-oxide and diethyl carbonate dissolved in LiPF ₆ at a mixing ratio of 50:50 was used at 1 mol / L.

Example 6 As an electrolyte for the lithium ion coin-type battery 10,
2-methyl-1,3,2-dioxaphosphorane-2
A mixture ratio of oxide and diethyl carbonate of 50:
A mixture obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixed solution of 50 was used.

Comparative Example 1 As an electrolyte for the lithium ion coin battery 10,
A mixture of ethylene carbonate (EC) and diethyl carbonate at a mixing ratio of 50:50 was prepared by dissolving 1 mol / l of LiPF ₆ .

For the non-aqueous electrolyte secondary batteries of Examples 1 to 6 and Comparative Example 1, a charging current of 1 mA and a cut-off voltage of 3.
Perform constant current charging up to 2V, then discharge current 3m
A, constant current discharge was performed up to a final voltage of 2.5 V, and a charge / discharge test was performed. In the charged state, the capacity after storage at 60 ° C. for 20 days and the recovery capacity after storage were measured.
Shown in

[0029]

[Table 1]

From Table 1, it can be seen that this embodiment is excellent in the capacity after storage and the recovery capacity after storage.

Example 7 As an electrolyte for the lithium ion coin-type battery 10,
Using a mixture of 1,3,2-dioxaphosphorane-2-oxide and diethyl carbonate,
The compounding ratio of 2-dioxaphosphorane-2-oxide was 1%.

Example 8 As an electrolyte for the lithium ion coin-type battery 10,
Using a mixture of 1,3,2-dioxaphosphorane-2-oxide and diethyl carbonate,
The compounding ratio of 2-dioxaphosphorane-2-oxide was 5%.

Example 9 As an electrolyte for the lithium ion coin-type battery 10,
Using a mixture of 1,3,2-dioxaphosphorane-2-oxide and diethyl carbonate,
The compounding ratio of 2-dioxaphosphorane-2-oxide was set to 20%.

Example 10 The electrolyte of the lithium ion coin battery 10 was as follows:
Using a mixture of 1,3,2-dioxaphosphorane-2-oxide and diethyl carbonate,
The compounding ratio of 2-dioxaphospholane-2-oxide was 40%.

Example 11 As an electrolytic solution of the lithium ion coin battery 10,
Using a mixture of 1,3,2-dioxaphosphorane-2-oxide and diethyl carbonate,
The compounding ratio of 2-dioxaphosphorane-2-oxide was set to 60%.

Example 12 The electrolyte of the lithium ion coin battery 10 was as follows:
It uses only 1,3,2-dioxaphosphorane-2-oxide.

The non-aqueous electrolyte secondary batteries of Examples 7 to 12 were charged at a constant current of 1 mA and a final voltage of 4.2 V, and then charged at a discharge current of 3 mA and a final voltage of 2.5 V. A constant current discharge was performed, and a charge / discharge test was performed. Capacity after storage at 60 ° C for 20 days in charged state,
The recovery capacity after storage was measured, and the results are shown in Table 2.

[0038]

[Table 2]

From Table 2, it can be seen that the compounding ratio of the 1,3,2-dioxaphosphorane-2-oxide derivative is 1% or more,
It is preferably 50% or less, more preferably 5% or more and 50% or less. On the other hand, if it exceeds 60%, the viscosity increases,
It is not preferable because the capacity is reduced. As a factor that the capacity after storage and the recovery capacity after storage increase and the self-discharge rate decreases, 1,3,2-dioxaphosphorane-2-oxide decomposes LiPF ₆ used as a lithium salt. Probably because it is suppressed by being present.

In this embodiment, some derivatives of 1,3,2-dioxaphosphorane-2-oxide have been described, but other derivatives may be used. In addition, although diethyl carbonate was used as the mixed solvent, other carbonates such as dimethyl carbonate, dipropyl carbonate,
Ethyl acetate, methyl propionate and the like can also be used. Also, one kind of carbonaceous material was used as carbon,
It goes without saying that other carbonaceous materials may be used.

In this example, a coin-type non-aqueous electrolyte secondary battery was prepared to verify the present invention. However, the present invention was applied to a battery having another shape such as a rectangular battery or a battery having a spiral electrode configuration. Of course, it may be used.

Second Embodiment Next, as a second embodiment, a nonaqueous electrolyte secondary battery using propane sultone or butane sultone as the solvent for the electrolyte will be described. The second embodiment differs from the first embodiment in that the solvent for the electrolytic solution is propane sultone, instead of the 1,3,2-dioxaphosphorane-2-oxide derivative, or Is different in using butane sultone,
The configuration of the negative electrode active material, the positive electrode active material, and the battery to be used are the same as those described in the first embodiment, and description thereof will be omitted.

As the organic solvent, any of those conventionally known can be used. For example, propylene carbonate,
Esters such as ethylene carbonate and γ-butyl lactone; ethers such as diethyl ether, tetrahydrofuran, substituted tetrahydrofuran, dioxolan, pyran and derivatives thereof, dimethoxyethane and diethoxyethane, and 3-methyl-2-oxazolidinone such as 3-methyl-2-oxazolidinone Examples thereof include substituted 2-oxazolidinones, sulfolane, methylsulfolane, acetonitrile, propionitr and the like, and these are used alone or as a mixture of two or more kinds of sultone. Further, as the electrolyte, lithium perchlorate, lithium borofluoride, lithium phosphofluoride, lithium aluminate, lithium halide, lithium trifluoromethanesulfonate and the like can be used.

Example 13 As an electrolyte for the lithium ion coin-type battery 10,
Mixing ratio of propane sultone and diethyl carbonate 5
A solution obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixture of 0:50 was used.

Example 14 The electrolyte of the lithium ion coin battery 10 was as follows:
Mixing ratio of propane sultone and diethyl carbonate 4
A solution obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixture of 0:60 was used.

Example 15 As an electrolyte for the lithium ion coin battery 10,
Mixing ratio of propane stron and diethyl carbonate 3
A mixture obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixture of 0:70 was used.

Example 16 As an electrolyte for the lithium ion coin battery 10,
Mixing ratio of propane stron and diethyl carbonate 2
A solution obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixture of 0:80 was used.

Example 17 As an electrolytic solution of the lithium ion coin battery 10,
Mixing ratio of propane stron and diethyl carbonate 1
A solution obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixture of 0:90 was used.

Example 18 As an electrolyte for the lithium ion coin-type battery 10,
Mixing ratio of propane stron and diethyl carbonate 5:
A solution obtained by dissolving 1 mol / l of LiPF _{6 in} a mixed solution of 95 was used.

Example 19 The electrolyte of the lithium ion coin battery 10 was as follows:
Mixing ratio of propane stron and diethyl carbonate 1:
A solution obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixed solution of 99 was used.

Example 20 The electrolyte of the lithium ion coin battery 10 was as follows:
Mixing ratio of butane sultone and diethyl carbonate 50:
A mixture obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixed solution of 50 was used.

Comparative Example 2 As an electrolyte for the lithium ion coin battery 10,
Mixing ratio of ethylene carbonate and diethyl carbonate 50: 5
A mixture obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixed solution of 0 was used.

Comparative Example 3 As an electrolyte for the lithium ion coin-type battery 10,
Mixing ratio of propane stron and diethyl carbonate 6
A solution obtained by dissolving LiPF ₆ at a ratio of 1 mol / liter in a mixture of 0:40 was used.

The non-aqueous electrolyte secondary batteries of Examples 13 to 20 and Comparative Examples 2 and 3 had a charging current of 1 m
A, constant current charging up to a final voltage of 4.2 V was performed, and then a constant current discharge was performed up to a discharge current of 3 mA and a final voltage of 2.5 V to perform a charge / discharge test. 60 when charged
The storage capacity after storage at 20 ° C. for 20 days and the recovery capacity after storage were measured, and the results are shown in Tables 3 and 4.

[0055]

[Table 3]

[0056]

[Table 4]

As a result of the above test, it is understood that the present embodiment has an excellent capacity after storage. The compounding ratio is preferably 1% or more and 50% or less, more preferably 5% or more and 50% or less. It is also possible to use sultone derivatives, and methylated or methoxylated sultone can be used. In addition, carbon is 1
Although various kinds of carbonaceous materials were used, it is needless to say that other carbonaceous materials may be used.

In this example, a coin-type non-aqueous electrolyte secondary battery was prepared to verify the present invention. However, the present invention was applied to batteries of other shapes such as a square battery or a battery having a spiral electrode configuration. Of course, it may be used.

[0059]

As is apparent from the above description, by adding 1,3,2-dioxaphosphorane-2-oxide, propane sultone, and butane sultone as the electrolytic solution, the volume after storage and the volume after storage are reduced. A non-aqueous electrolyte secondary battery having an increased recovery capacity and a small self-discharge rate can be formed.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a non-aqueous electrolyte secondary battery according to the present invention.

FIG. 2 is a chemical formula of a 1,3,2-dioxaphosphorane-2-oxide derivative used in the present invention.

FIG. 3 is a chemical formula of 1,3,2-dioxaphosphorane-2-oxide used in the present invention.

[Explanation of symbols]

1 ... Negative electrode cup, 2 ... Negative electrode pellet, 3 ... Separator,
4: Positive electrode pellet 5: Gasket, 6: Positive electrode can, 10: Lithium ion coin cell battery

Claims (3)

[Claims] 1. A non-aqueous electrolyte secondary battery, wherein 1,3,2-dioxaphosphorane-2 is used as an electrolyte solvent.
-A non-aqueous electrolyte secondary battery comprising an oxide derivative in a mixing ratio of 5% or more and 50% or less. 2. A non-aqueous electrolyte secondary battery, wherein propane sultone is mixed in an electrolyte solvent at a mixing ratio of 5% or more, and
% Of the non-aqueous electrolyte secondary battery. 3. A non-aqueous electrolyte secondary battery, wherein butane sultone is mixed in an electrolyte solvent at a mixing ratio of 5% or more and 50% or more.
A nonaqueous electrolyte secondary battery characterized by being contained in the following range.